However, PP officials have repeatedly denied the El Pais documents. In an interview aired on 13tv last night in Spain, the man at the center of the scandal, former treasurer Luis Bárcenas, said he had done nothing wrong and had earned his money legally.

According to a transcript of the interview published on El Economista, Bárcenas suggested that the handwritten checking accounts were a forgery, created by "someone close to the party". He said he would be ready for a calligraphy test to certify that it is not his handwriting.

On the same show, PP secretary general María Dolores de Cospedal that some "half-truths" appeared in the documents.

The allegation that someone linked to PP could have faked the notes seems to tie in with Rajoy's own bizarre admission that some part of the scandal is in fact true. From El Pais yesterday:

“I repeat what I said Saturday: everything that has been said about me and my colleagues in the party is untrue, except for some things that have been published by some media outlets.”

Whether the donations were actually illegal is actually a matter of debate. The BBC notes that until 2007, Spanish political parties were allowed to receive anonymous donations, while El Pais says that as all donations were under 120,000 euros they may be exempt from tax charges.

However, in a country that has suffered badly since the 2008 crisis, any hint of corruption involving Spain's once booming construction industry would be extremely damaging for the PP.

The party has threatened El Pais with legal action over the publication. Speaking to 13tv yesterday, Cospedal said the newspaper had created "great social alarm" with a "photocopy of a photocopy of something nobody can verify."